Damping device and method

ABSTRACT

The method and device of the present invention reduces the pulsation of fluid from a pump. The damping device and method works on either the positive pressure or negative pressure side of the pump. Under positive pressure the device is attached downstream from the outlet port of a pump, the device having an input port in fluidic communication with the outlet port of the pump, an outlet port, an outer wall with an opening, and a membrane covering the opening, the outer wall of the device and the membrane forming a contained volume. As fluid from the outlet port of the pump passes into the device, it enters the contained volume which expands and contracts, thereby vitiating the pulsations in the fluid flow downstream of the device. Alternatively, under negative pressure the device is attached upstream from the inlet port of a pump.

PRIORITY STATEMENT

This non-provisional application claims priority based upon prior U.S. Provisional Patent Application Ser. No. 61/583,008 filed Jan. 4, 2012 in the name of Matthew F. Bartlett entitled “Pneumatic Damping Device,” the disclosure of which is incorporated herein in its entirety by reference as if fully set forth herein.

FIELD OF THE INVENTION

The present invention generally relates to a device that converts pulsed fluid flow into pulsation-free fluid flow.

BACKGROUND OF THE INVENTION

Fluid pumps utilize various methods to generate flow and pressure. For example, certain types of pumps use diaphragms or rotary vanes to pump fluids. However, the mechanisms by which these and other pumps move the fluid often result in pulsations in the output profile of the fluid. To make matters worse, the pulsation is typically more noticeable at slower pump speeds. Many applications require smooth output profiles or output profiles that are substantially free of pulsations and, as a result, pumps that generate pulsations are not desirable.

Generally, complicated, expensive, and power-consuming flow controlling devices, such as a mass flow controllers (MFCs), have been used to reduce or eliminate output pulsation. These devices typically utilize closed-loop electronic control of a proportional valve to stabilize the output profile. However, this control process also creates additional backpressure in the pumping system, requiring the pump to draw even more power to maintain the desired flow rate. Although they can be effective in reducing pulsations in the fluid output, MFCs' expense and power consumption negate their use in both lower-cost and battery-powered applications.

There is a need therefore for a method and device to reduce pulsation in the output profile of fluid from a pump while controlling cost, power consumption and ease of use.

SUMMARY OF THE INVENTION

The device of the present invention reduces the pulsation of fluid from a pump in an economical, efficient manner. The damping device works on either the positive pressure or negative pressure side of the pump.

Under positive pressure, the device is attached downstream from the outlet port of a pump. The device has an inlet port in fluidic communication with the outlet port of the pump, an outlet port, an outer wall with an opening, and a membrane covering the opening, the outer wall of the device and the membrane forming a contained volume. As fluid from the outlet port of the pump passes into the device, it enters the contained volume which expands and contracts through movement of the membrane, thereby vitiating the pulsations in the fluid caused by the pump. The fluid then exits through the outlet port.

Under negative pressure, the device is attached upstream from the inlet port of a pump. Once again, the device has an outlet port in fluidic communication with the inlet port of the pump, an inlet port, an outer wall with an opening, and a membrane covering the opening, the outer wall of the device and the membrane forming a contained volume. As fluid moves through the inlet of the device it enters the contained volume where it expands and contracts through movement of the membrane, thereby vitiating the pulsations in the fluid caused by the pump. The fluid then exits through the outlet port and enters the inlet port of the pump.

The membrane may be made of a variety of materials and, in certain embodiments, the outer wall of the device is comprised entirely of the membrane. Certain embodiments of the damping device of the present invention utilize an orifice at the outlet of the device to create backpressure.

The foregoing has outlined rather broadly certain aspects of the present invention in order that the detailed description of the invention that follows may better be understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is and exterior top view of the damping device;

FIG. 2 is a cross-sectional side view of damping device;

FIG. 3 is an exterior top view of two damping devices in a single unit;

FIG. 4 shows mass flow meter data from an un-damped diaphragm pump; and

FIG. 5 shows mass flow meter data from a diaphragm pump with the damping device.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a device that reduces the pulsation of fluid passing through a pump. The configuration and use of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of contexts other than the simple pumping of a fluid. Accordingly, the specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention. In addition, the following terms shall have the associated meaning when used herein:

“fluid” means and includes any gas, liquid or plasma or any other phase of matter which deforms under an applied shear stress;

“pulse” or “pulsation” means and includes a rapid, transient change in the amplitude of a signal from a baseline value to a higher or lower value, followed by a rapid return to the baseline value; and

“pump” means and includes any device that moves fluid by mechanical action.

Referring now to FIG. 1 which shows damping device 1 which comprises housing 2, flexible membrane 3, fluid inlet 4, and fluid outlet 5. Housing 2 can be constructed from any suitable material known in the art, including, without limitation, plastic, aluminum, and steel. Flexible membrane 3 may also be selected from materials known in the art, including, without limitation, natural rubber, latex, neoprene, nitrile, silicone and viton.

Referring now to FIG. 2 which show contained volume 7. As flexible membrane 3 moves, volume 7 expands and contracts, causing volume 7 to be variable. Membrane 3 may comprise an open sheet that is adhered to or clamped into place by fasteners 2, each of which may be removable or fixed. In some embodiments, membrane 3 is a single layer of material fastened into place by a two separate fasteners 2 that are bound together. This embodiment works well in both positive pressure and negative pressure conditions. Alternatively, material 3 may be a tubular or bag shape that is a single unit around its circumference. In this case, under negative pressure conditions, fastener 2 may be a frame structure contained inside material 3. Alternatively, fastener 2 can be outside of, but bound to, material 3. In either case, the function of fastener 2 is to keep material 3 from collapsing into itself when the pressure inside device 1 is less than the pressure outside device 1.

The size of the enclosure of device 1 (i.e. the portions of the walls of device 1 but excluding material 3) relative to material 3 is highly variable and several designs and ratios can function in various embodiments of this invention. As a non-limiting example, FIG. 1 shows damping device 1 with a relative surface area ratio of the enclosure to material 3 of approximately 4:1. However, larger or an increased number of ports in the enclosure of device 1 would change the ratio to 2:1, 1:1, or even 1:4. In fact, in one embodiment of this invention, membrane 3 is a tubular material and an enclosure is not required.

The embodiment of the invention depicted in FIG. 2 includes an optional restrictive orifice 6. Instead of being mounted inside of device 1 as depicted, restrictive orifice 6 may be connected by tubing downstream of the device 5. While the placement of restrictive orifice 6 is not critical, it must be placed on the outlet side of device 1 and contained volume 7.

In operation, the surface area of flexible membrane 3 oscillates at approximately the same frequency as the output profile of the pump to which it is attached. Contained volume 7 serves as a reservoir to equalize the output profile. Orifice 6 optionally provides back pressure, increasing the averaging effect of the contained volume 7. Optimally, orifice 6 is specifically sized for the desired flow range and only contributes approximately 3% of the total power consumed by the pump to maintain the desired flow rate. While orifice 6 is optional, it may provide a unit capacity advantage by restricting the free flow of fluid and thereby allowing more “pulses” to be pneumatically averaged by damping device 1, and thereby generating a smoother output.

The effect of the orifice 6 depends on various flow parameters such as, for example, pressure, volume 7, membrane 3 surface area, and pulse oscillation frequency. Orifice 6 may be particularly helpful in the worst-case flow control scenario where the diaphragm pump speed is very slow. In this slow RPM situation, the pulses are large in amplitude and farther apart in frequency. The larger the surface area of membrane 3, the less the need for orifice 6; thus orifice 6 assists in reducing the overall size of damping device 1.

Referring now to FIG. 3 depicting an embodiment of the present invention in which more than one damping device is contained in a single unit. As a non-limiting example, damping device 8 possesses two separate fluid volumes each with a separate acting membrane 3, two fluid inlet connections 4, and two fluid outlet ports 5 with optional restrictive orifices. Note that, in this embodiment, fastener 2 is a continuous fastener which covers both membranes 3 but, in other embodiments, the fasteners 2 may be separated into two or more parts.

FIG. 4 is a measurement from a mass flow meter showing the raw, un-damped output profile from a diaphragm pump. Pressure is depicted along the vertical axis and time is depicted along the horizontal axis. As can be seen, there are rapid, transient changes in the amplitude of the pressure signal from a baseline value to a lower value, followed by a rapid return to the baseline value.

FIG. 5 is a measurement of the same diaphragm pump shown in FIG. 4, under identical operating parameters but, in this case, one embodiment of the device of the present invention is attached downstream from the pump and the measurement is taken at the outlet port of the device. Once again, pressure is depicted along the vertical axis and time is depicted along the horizontal axis. It is evident that the pulsation of the fluid is virtually eliminated and a more precise calculation shows reduction in pulsation of at least 400:1.

While the present device has been disclosed according to the preferred embodiment of the invention, those of ordinary skill in the art will understand that other embodiments have also been enabled. Even though the foregoing discussion has focused on particular embodiments, it is understood that other configurations are contemplated. In particular, even though the expressions “in one embodiment” or “in another embodiment” are used herein, these phrases are meant to generally reference embodiment possibilities and are not intended to limit the invention to those particular embodiment configurations. These terms may reference the same or different embodiments, and unless indicated otherwise, are combinable into aggregate embodiments. The terms “a”, “an” and “the” mean “one or more” unless expressly specified otherwise. The term “connected” means “communicatively connected” unless otherwise defined.

When a single embodiment is described herein, it will be readily apparent that more than one embodiment may be used in place of a single embodiment. Similarly, where more than one embodiment is described herein, it will be readily apparent that a single embodiment may be substituted for that one device.

In light of the wide variety of possible fluid damping devices available, the detailed embodiments are intended to be illustrative only and should not be taken as limiting the scope of the invention. Rather, what is claimed as the invention is all such modifications as may come within the spirit and scope of the following claims and equivalents thereto.

None of the description in this specification should be read as implying that any particular element, step or function is an essential element which must be included in the claim scope. The scope of the patented subject matter is defined only by the allowed claims and their equivalents. Unless explicitly recited, other aspects of the present invention as described in this specification do not limit the scope of the claims. 

I claim:
 1. A device comprising: an outer casing with an opening in an exterior wall, wherein said opening is covered by a membrane, said membrane and said outer casing creating a constrained volume, wherein said membrane is configured to expand when pressure inside said constrained volume is greater than pressure outside said constrained volume and to retract when pressure outside said constrained volume is greater than pressure inside said constrained volume; an inlet port configured to allow fluid into said constrained volume; and an outlet port configured to allow fluid out of said constrained volume.
 2. The device of claim 1, further comprising a restrictive orifice downstream of said outlet port.
 3. The device of claim 1, wherein said membrane is natural rubber.
 4. The device of claim 1, wherein said membrane is latex.
 5. The device of claim 1, wherein said membrane is silicone.
 6. A method of damping fluid pulsations from the outlet port of a pump comprising: passing fluid through an inlet port into a contained volume, said contained volume created by an outer casing with an opening in an exterior wall and a membrane covering said opening; configuring said membrane such that it protrudes beyond said exterior wall when pressure of said fluid inside said contained volume is greater than pressure outside said contained volume and recedes into said contained volume when pressure outside said contained volume exceeds pressure of said fluid inside said contained volume; and thereafter passing said fluid through an outlet port.
 7. The method of claim 6, further comprising passing said fluid through a restrictive orifice downstream of said outlet port.
 8. The method of claim 6, wherein said membrane is natural rubber.
 9. The method of claim 6, wherein said membrane is latex.
 10. The method of claim 6, wherein said membrane is silicone.
 11. A device damping fluid pulsations from the outlet port of a pump comprising: means for containing fluid with an opening in an exterior wall, wherein said opening is covered by a membrane, said membrane and said means for containing fluid creating a constrained volume; means for allowing fluid into said constrained volume; means for allowing fluid out of said constrained volume; and wherein said membrane is configured to expand when pressure inside said constrained volume is greater than pressure outside said constrained volume and to retract when pressure outside said constrained volume is greater than pressure inside said constrained volume.
 12. The device of claim 11, further comprising means for restricting flow of said fluid into said inlet port.
 13. The device of claim 11, wherein said membrane is natural rubber.
 14. The device of claim 11, wherein said membrane is latex.
 15. The device of claim 11, wherein said membrane is silicone. 